Mobile station, base station, mobile communication system, and communication method

ABSTRACT

A mobile station, a base station, a mobile communication system and a communication method enabling operations associated with simultaneous uplink reception in multiple stations to be simplified are provided. The base station includes a transmission timing determining unit determining a transmission timing based on scheduling conducted upon a data transmission request from a mobile station and notifying the mobile station of the transmission timing, and a receiving unit receiving data in accordance with the transmission timing.

This Application is a Continuation Application of U.S. application Ser.No. 12/064,578 filed Apr. 10, 2009, which is a National Stage ofPCT/JP2006/316342 filed Aug. 21, 2006 which claims priority fromJapanese Patent Application No. 2005-241907 filed Aug. 23, 2005, thedisclosures of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a mobile station, a base station, amobile communication system and a communication method.

BACKGROUND ART

The present invention is applicable to radio communication systems forradio packet transmission over an uplink in Evolved UTRA and the fourthgeneration mobile radio communication scheme.

Among these systems, for example, in Evolved UTRA (UMTS (UniversalMobile Telecommunications System) Terrestrial Radio Access) defined byan international standardization organization (3GPP), improvement of thedata rate and the frequency efficiency at cell edges is one importantrequirement. For the improvement of the data rate and the frequencyefficiency at cell edges, macro-diversity is one important technique forpacket synthesizing between different base stations (inter-cell) orbetween different sectors within the same base station.

For example, uplink s oft -handover between cells can increase the datarate at cell edges to about 10-15% compared to hard-handover.

For this reason, inter-cell macro-diversity is an effective techniquefrom the viewpoint of improved user throughput at cell edges.

Non-patent document 1: 3PPG TR 25.896

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

However, the above-mentioned prior art may have some problems aspresented below. For example, as illustrated in FIG. 1, when a mobilestation performs the soft-handover to a serving base station or aprimary base station (serving node B) and a non-serving base station ora sub base station (non-serving node B), it must receive downlinksignaling channels from multiple cell sites simultaneously. Then, themobile station controls packet scheduling and HARQ (Hybrid AutomaticRepeat request) based on the received downlink signaling channels fromthe multiple cell sites. In other words, from the viewpoint of thepacket scheduling and the HARQ, the downlink signaling channels from theserving base station are indifferent from and are not differentiatedfrom the downlink signaling channels from the non-serving base station.In conventional soft-handover, signaling channels from multiple basestations are all indifferently handled, and the packet scheduling andthe HARQ are controlled in such a manner.

In packet transmission, packet related control such as the packetscheduling and the HARQ is carried out by a base station. A mobilestation cannot have merits of the handover until it receives theinformation from multiple base stations and controls the packetscheduling and the HARQ. Thus, the mobile station has to receive twosignals simultaneously. Such a condition of simultaneous reception fromtwo base stations is called a soft-handover condition. Here, the mobilestation performs the handover if an average reception level difference(path loss difference) from two base stations becomes small enough tofall within a certain threshold. In this case, the base station havingthe higher average reception level is the serving base station while thebase station having the lower average reception level is the non-servingbase station. In cases of simultaneous reception from three or more basestations, the base station having the highest average reception level isthe serving base station while the other base stations are thenon-serving base stations.

In the soft-handover condition, at least two base stations control thescheduling and the HARQ, and the feedback information is transmitted toa mobile station. Thus, the mobile station must receive the feedbackinformation from the at least two base stations.

Also, an associated DPCH (Dedicated Physical Channel) is required toreceive the feedback information. Even if there is no transmitted dataover a certain time period, the associated DPCH must be transmitted. Asa result, a base station must receive a number of associated DPCHscorresponding to W-CDMA simultaneously. The non-serving base stationalso assigns data channel transmissions for other handover users. As aresult, the serving base station only has to perform data channeldemodulation on mobile stations assigned data channel transmissionswhile the non-serving base station must perform not only the datachannel demodulation assigned for mobile stations by the serving basestation but also the data channel demodulation assigned for other mobilestations by the non-serving base station itself as the serving basestation and thus must receive signals from two users.

Furthermore, since the reception timing may differ depending on thelocation of the mobile stations, the associated DPCH and a shared datachannel must be received at different timings.

As a result, the soft-handover can improve user throughput while thecontrol is complicated.

The present invention is intended to eliminate the above-mentionedproblems. One object of the present invention is to provide a mobilestation, a base station, a mobile communication system and acommunication method for enabling simultaneous reception of multiplestations over the uplink to be simplified.

Means for Solving the Problem

In order to eliminate the above-mentioned problems, according to oneembodiment of the present invention, a mobile station includes a datatransmission request transmitting unit transmitting a data transmissionrequest; a transmission timing notifying unit notifying a serving basestation and a non-serving base station of a transmission timing reportedfrom the serving base station; and a data transmitting unit transmittingdata to the serving base station and the non-serving base station basedon the transmission timing. According to this embodiment, the mobilestation can notify the serving base station and the non-serving basestation of the transmission timing and transmit data in accordance withthe transmission timing.

In another embodiment of the present invention, a base station includesa transmission timing determining unit determining a transmission timingbased on scheduling conducted upon a data transmission request from amobile station and notifying the mobile station of the transmissiontiming; and a receiving unit receiving data from the mobile station inaccordance with the transmission timing.

According to this embodiment, it is possible to conduct scheduling forthe mobile station, determine the transmission timing and receive datain accordance with the transmission timing.

In another embodiment of the present invention, a base station includesa receiving unit receiving data in accordance with a transmission timingreported from a mobile station; and a packet forwarding unit forwardingdecoded data to a serving base station for the mobile station if noerror is detected in the data.

According to this embodiment, it is possible to receive data inaccordance with the transmission timing reported from the mobile stationand forward decoded data to the serving base station for the mobilestation if no error is detected in the data. In other words, if an erroris detected in the data, the non-serving base station waits.

In another embodiment of the present invention, a mobile communicationsystem includes a serving base station, a non-serving base station and amobile station conducting handover between the serving base station andthe non-serving base station. The mobile station includes a datatransmission request transmitting unit issuing a data transmissionrequest; a transmission timing notifying unit notifying the serving basestation and the non-serving base station of a transmission timingreported from the serving base station; and a data transmitting unittransmitting data to the serving base station and the non-serving basestation based on the transmission timing. The serving base stationincludes a transmission timing determining unit, upon the datatransmission request from the mobile station, conducting scheduling,determining the transmission timing and notifying the mobile station ofthe transmission timing; and a receiving unit receiving data inaccordance with the transmission timing. The non-serving base stationincludes a receiving unit receiving data in accordance with thetransmission timing reported from the mobile station; and a packetforwarding unit forwarding decoded data to the serving base station ifno error is detected in the data.

According to this embodiment, the mobile station can notify the servingbase station and the non-serving base station of the transmission timingand transmit data in accordance with the transmission timing. Also, theserving base station can conduct scheduling for the mobile station,determine the transmission timing and receive data in accordance withthe transmission timing. Also, the non-serving base station can receivedata in accordance with the transmission timing reported from the mobilestation and forward decoded data to the serving base station for themobile station if no error is detected in the data.

In another embodiment of the present invention, there is a communicationmethod for use in a mobile communication system including a serving basestation, a non-serving base station and a mobile station conductinghandover between the serving base station and the non-serving basestation, the method including the steps of: at the mobile station,issuing a data transmission request; notifying the serving base stationand the non-serving base station of a transmission timing reported fromthe serving base station; and transmitting data to the serving basestation and the non-serving base station based on the transmissiontiming; at the serving base station, conducting scheduling upon the datatransmission request; determining the transmission timing; notifying themobile station of the transmission timing; and receiving data inaccordance with the transmission timing; and at the non-serving basestation, receiving data in accordance with the transmission timingreported from the mobile station; detecting an error in the data; andforwarding decoded data to the serving base station if no error isdetected in the data.

According to this embodiment, the mobile station can notify the servingbase station and the non-serving base station of the transmission timingand transmit data in accordance with the transmission timing. Also, theserving base station can conduct scheduling for the mobile station,determine the transmission timing and

receive data in accordance with the transmission. timing. Also, thenon-serving base station can receive data in accordance with thetransmission timing reported from the mobile station and forward decodeddata to the serving base station for the mobile station if no error isdetected in the data. The mobile station performs some control based ononly a signaling channel from the serving base station.

Advantage of the Invention

According to the embodiments of the present invention, it is possible toprovide a mobile station, a base station, a mobile communication systemand a communication method for enabling simultaneous reception ofmultiple stations over the uplink to be simplified.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating a soft-handover condition;

FIG. 2 is a schematic view illustrating a mobile 30 communication systemaccording to one embodiment of the present invention;

FIG. 3 is a block diagram illustrating an exemplary W-CDMA based mobilecommunication system;

FIG. 4 is a block diagram illustrating a mobile station according to oneembodiment of the present invention;

FIG. 5A is a block diagram illustrating a serving base station accordingto one embodiment of the present 5 invention;

FIG. 5B is a block diagram illustrating a non-serving base stationaccording to one embodiment of the present invention; and

FIG. 6 is a sequence diagram illustrating an operation of a mobilecommunication system according to one embodiment of the presentinvention.

LIST OF REFERENCE SYMBOLS

-   10: mobile communication system 15-   100: mobile station-   200: base station-   200 ₁: serving base station-   200 ₂: non-serving base station

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described with reference tothe drawings. Throughout the drawings, the same reference symbols may beused for objects having the same function, and iterative descriptionsthereof will be omitted.

A mobile communication system according to an embodiment of the presentinvention will be described with reference to FIG. 2.

A mobile communication system 20 according to this embodiment includes amobile station 100 and base stations 200 ₁ and 200 ₂.

In this embodiment, the mobile station 100 is in the soft-handovercondition between the serving base station 200 ₁ and the non-servingbase station 200 ₂ and can communicate with the serving base station 200₁ and the non-serving base station 200 ₂ simultaneously.

In this embodiment, the mobile station 100 performs scheduling controlwhere data channel transmissions are assigned for mobile stations by asingle base station, that is, the serving base station 200 ₁, andretransmission control where if a packet is not successfully decoded inthe base station, the packet is retransmitted.

When the serving base station 200 ₁ has conducted the scheduling and theuser assignment, it notifies the mobile station 100 of a transmissiontiming indicative of the transmission timing of data and a combinationMCS (Modulation and channel Coding Scheme) of the modulation scheme andthe channel coding rate as reservation information.

Upon receipt of the reservation information from the serving basestation 200 ₁, the mobile station 100 transmits some information such asconfirmation information to confirm the assignment, the transmissiontiming and the MCS to the serving base station 200 ₁ and the non-servingbase station 200 ₂ in an associated control channel such as theassociated DPCH.

The mobile station 100 transmits data to the serving base station 200 ₁and the non-serving base station 200 ₂ in a data channel in accordancewith the transmission timing.

The non-serving base station 200 ₂ only performs decoding of receivedpackets and reception of HARQ. If the received packet is successfullydecoded, the non-serving base station 200 ₂ forwards the packet to theserving base station 200 ₁. If the packet is not successfully decoded,the non-serving base station 200 ₂ temporarily stores it and waits.

The serving base station 200 ₁ performs demodulation and decoding on thereceived data channel. If the received data channel is not successfullyreceived, the serving base station. 200 ₁ temporarily stores it andwaits. On the other hand, if the reception is successful from thenon-serving base station 200 ₂, the serving base station 200 ₁determines whether the transmitted packet is received. If the packet isnot received from the non-serving base station 200 ₂ during apredetermined time period, the serving base station 200 ₁ requests aretransmission operation by the mobile station of interest. In thiscase, the serving base station 200 ₁ transmits retransmission requestinformation to the mobile station 100. The terminology “retransmissionoperation” used herein refers to a series of operations where inresponse to detection of a decoding error in the decoding of packets ina base station, the base station transmits the retransmission requestinformation to the mobile station and then the mobile stationretransmits the same packet to the base station.

In the case where the retransmission is requested, the serving basestation 200 ₁ and the non-serving base station 200 ₂ perform the HARQoperation and combine the retransmitted packet with the previouslyreceived packet with the decoding error.

In this embodiment, a downlink control channel (feedback signaling) istransmitted from only the serving base station 200 ₁ and is received atthe mobile station 100. The non-serving base station 200 ₂ does nottransmit the downlink control channel (feedback signaling).

Thus, no control information indicative of the retransmission request istransmitted from the non-serving base station 2002 to the mobile station100, and the mobile station 100 does not have to receive feedbackchannels from multiple sites simultaneously. As a result, it is possibleto simplify the reception and retransmission control of the downlinkcontrol channels.

In the W-CDMA, as illustrated in FIG. 3, some information associatedwith a transmission acknowledgement signal (ACK) and/or a retransmissionrequest signal (NACK) is transmitted from the both base station, thatis, the serving base station and the non-serving base station to themobile station.

In the W-CDMA, the serving base station performs the scheduling andtransmits the assignment information to the mobile station and thenon-serving base station. The mobile station transmits a data channel inaccordance with the assignment information.

The data channel transmitted from the mobile station is received at bothbase stations, and both base stations perform demodulation and decoding.If the reception succeeds at either of the base stations, the datachannel can be combined at any upper station. As a result, theretransmission operation does not have to be conducted. Only if neitherof the base stations successfully receives the data channel, theretransmission operation is conducted. In this case, ACK/NACKinformation is transmitted from both the base stations to the mobilestation.

In this embodiment, on the other hand, no ACK/NACK information istransmitted from the non-serving base station 200 ₂ to the mobilestation 100. Next, the mobile station 100 according to this embodimentwill be described with reference to FIG. 4.

In this embodiment, the mobile station 100 includes a data transmissionrequest transmitting unit 102, a control unit 104 coupled to the datatransmission request transmitting unit 102 and serving as a transmissiontiming reporting unit, and a data transmitting unit 106 coupled to thecontrol unit 104.

Upon occurrence of transmitted data, the data transmission requesttransmitting unit 102 transmits a data transmission request to theserving base station 200 ₁.

The control unit 104 reports a transmission timing received from theserving base station 200 ₁ to the serving base station 200 ₁ and thenon-serving base station 200 ₂.

The data transmitting unit 106 transmits the data to the serving basestation 200 ₁ and the non-serving base station 200 ₂ based on thetransmission timing received from the serving base station 200 ₁. Next,the base station 200 according to this embodiment will be described withreference to FIGS. 5A and 5B.

In this embodiment, although the base station 200 will be described bydividing it into the serving base station 200 ₁ and the non-serving basestation 200 ₂, the base station 200 includes both functions.

The serving base station 200 ₁ includes a receiving unit 202, a controlunit 204 coupled to the receiving unit 202, a selection combination unit206 coupled to the control unit 204 and a retransmission requestreporting unit 208.

The receiving unit 202 performs demodulation and decoding on. receivedpackets and conducts error detection. Also, if a retransmitted packet isreceived, the receiving unit 202 combines the retransmitted and originalpackets.

If the packet received at the receiving unit 202 includes some error,the control unit 204 waits during a predetermined time period todetermine whether a successfully received packet frame or IP packet isforwarded from the non-serving base station. If a successfully receivedpacket frame or IP packet is not forwarded from the non-serving basestation 200 ₂ within the predetermined time period, the control unit 204determines that the packet has not been successfully received at thenon-serving base station 200 ₂ as well and instructs the retransmissionrequest reporting unit 208 to issue a retransmission request. Thepredetermined time period is determined in advance based on the distancebetween the serving base station 200 ₁ and the non-serving base station200 ₂, the transfer rate and processing delay. For example, as thepackets are routed via a greater number of upper stations, theprocessing delay may increase. In other words, the predetermined timeperiod is determined based on the path condition.

The retransmission request reporting unit 208 transmits theretransmission request to the mobile station 100 in accordance with theinstruction from the control unit 204.

Upon receipt of the packet from or IP packet transmitted from thenon-serving base station 200 ₂, the selection combination unit 206performs selection combination on the packet. If the decoded packetframe or IP packet is received, the selection combination unit 206performs the selection combination.

The non-serving base station 200 ₂ includes a receiving unit 210, acontrol unit 212 coupled to the receiving unit 210, and a packetforwarding unit 214 30 coupled to the control unit 212.

The receiving unit 210 performs demodulation and decoding on packetstransmitted from the mobile station 100 and conducts error detection.Also, if a retransmitted packet is received, the receiving unit 210combines the packets.

The control unit 212 waits if the packet received at the receiving unit210 includes an error, and on the other hand, forwards the packet inunits of packet frames or IP packets to the serving base station 200 ₁via the packet forwarding unit 214 if the packet includes no error andthus can be successfully demodulated and decoded.

The packet forwarding unit 214 uses a Layer 2 (L2) address such as a MAC(Medium Access Control) address or a Layer 3 (L3) address such as an IPaddress to forward the successfully demodulated and decoded packet frameor packet frames in units of concatenated IP packets to the serving basestation 200 ₁ via a wired transmission channel or a backhaul. The packetforwarding unit 214 may forward it to the serving base station 200 ₁directly, or may forward it via an upper station.

Next, an exemplary operation of a mobile communication system accordingto this embodiment will be described with reference to FIG. 6. It isassumed that the serving base station 200 ₁ and the non-serving basestation 200 ₂ have been already determined for the mobile station 100.

The data transmission request transmitting unit 102 of the mobilestation 100 transmits some information indicative of the presence ofsome data to be transmitted to the serving base station 200 ₁ (stepS602).

The serving base station 200 ₁ performs scheduling in the control unit204 (step S604). In the case where a handover user is assigned, theserving base station 200 ₁ transmits reservation information to thehandover user (step S606). The reservation information may includeassignment information indicating that a handover user has been assignedsuch as an assigned time slot and frequency information, a transmissiontiming indicative of a timing for transmitting a shared data channel,MCS and others. In this manner, the mobile station can know that it hasbeen assigned.

Upon receipt of the reservation information, the mobile station 100transmits some information including acknowledge information foracknowledging that it has been assigned, the transmission timing, theMCS and others to the serving base station 200 ₁ and the non-servingbase station 200 ₂ in an associated control channel such as anassociated DPCH (steps 5608, S610). Since the transmission timing isreported in this manner before the transmission of shared data channels,the non-serving base station 200 ₂ can recognize the reception timing ofthe shared data channel of the handover user and MCS information inadvance. This is one feature of the present invention. Also, in thiscase, additional scheduling delay is acceptable to the mobile station100 (handover user).

In the non-serving base station 200 ₂, the associated DPCH must bereceived to receive a shared data channel.

For example, a common associated physical channel may be used as theassociated DPCH. This common associated physical channel is shared amonghandover users and is used commonly among the users. The commonassociated physical channel may be commonly used in a collection ofdedicated channels.

The users may be multiplexed in any one of several methods, for example,time multiplexing where the users are switched for individual subframesor packets, frequency multiplexing where the users are multiplexed infrequency areas, and code multiplexing where the multiple users can beaccepted by using different codes.

Also, the associated DPCH may be used. If the associated DPCH is used, adedicated channel or a common channel may be used.

The use of the dedicated channel has an advantage that the assigned usercan be assured of using it. On the other hand, the use of the commonchannel has an advantage that a greater number of users can be accepted.

If a common channel is used and a transmission scheme similar tofrequency diversity is adopted, all users can enjoy some reasonablereception quality. Also, the reception quality can be improved bycontrolling the transmission power.

As the multiplexing scheme among common channels, the above-mentionedtime multiplexing, frequency multiplexing or code multiplexing may beused.

The mobile station 100 transmits data in a shared data channel inaccordance with the transmission timing (steps S612, S614). Thetransmitted data are received at the serving base station 200 ₁ and thenon-serving base station 200 ₂.

The serving base station 200 ₁ and the non-serving base station 200 ₂decode received packets (steps 5616, S618).

The non-serving base station 200 ₂, if the packets have beensuccessfully demodulated and decoded, forwards the decoded packet frameor concatenated IP packets to the serving base station 200 ₁. It is onefeature of the present invention to forward the packet frame or IPpackets successfully decoded at the non-serving base station to theserving base station as mentioned above.

The non-serving base station 200 ₂, if the packets have not beensuccessfully decoded, takes no action.

On the other hand, the serving base station 200 ₁, if the packets havenot been successfully decoded, waits for the non-serving base station200 ₂ to forward the successfully received packet frame or concatenatedIP packets. The serving base station 200 ₁, if the successfully receivedpacket frame or concatenated IP packets are not forwarded during apredetermined time period, determines that the non-serving base station200 ₂ also failed to receive the packets and initiates theretransmission control.

Also, the non-serving base station 200 ₂, if the packets have not beensuccessfully received, may notify the serving base station 200 ₁ withsome information indicating that the packets have not been successfullyreceived. In this manner, the serving base station 2001 can initiate theretransmission control rapidly based on a packet reception result of theserving base station 200 ₁ itself.

According to this embodiment, the packet scheduling can be conductedonly between the mobile station and the serving base station. As aresult, the non-serving base station only has to decode a shared datachannel and does not have to transmit feedback information to the mobilestation. In this case, the non-serving base station may be notified ofMCS information and the reception timing of the shared data channel fromthe mobile station via a control channel such as an associated DPCH inadvance.

In the non-serving base station 200 ₂, in order to reduce the number ofcommon data channels and the associated DPCHs, UE (User Equipment) IDindicative of a transmitting user, the transmission timing and the MCSinformation may be received in a common associated physical channel inadvance. For example, the control unit 104 reports the transmissiontiming and the UE ID via a control channel commonly used among multiplemobile stations. Since the UE ID is included, the corresponding user canbe identified at the non-serving base station 200 ₂ even when thecontrol channel is commonly used among multiple users.

The non-serving base station 200 ₂ receives and decodes a successiveshared data channel (packet composite type HARQ at retransmission).Then, if no error is detected in CRC (Cyclic Redundancy Check), thenon-serving base station 200 ₂ forwards the decoded packet. For example,the non-serving base station 200 ₂ may use a L2 address or a L3 addressto forward the decoded packet to the serving base station 200 ₁. Sincethe shared data channel is associated with packet mode transmissionrather than circuit switching, the non-serving base station 200 ₂ doesnot have to have so many receiving cards such as boards.

According to this embodiment, the handover that can obtainmacro-diversity gain equivalent to the soft-handover withoutsimultaneous reception of feedback channels from multiple sites isachievable. In addition, a best effort type complementary HHO in theuplink can be achieved.

INDUSTRIAL APPLICABILITY

The mobile station, the base station, the mobile communication systemand the communication method according to the present invention can beapplied to mobile communication systems. This international patentapplication is based on Japanese Priority Application No. 2005-241907filed on Aug. 23, 2005, the entire contents of which are herebyincorporated by reference.

1. A mobile station comprising: a transmitter adapted to transmit a datatransmission request; wherein the transmitter transmits, to a first basestation and a second base station, transmission timing transmitted fromthe first base station; and transmits data to the first base station andthe second base station based on the transmission timing; and a receiveradapted to receive the transmission timing.
 2. The mobile stationaccording to claim 1, wherein the transmission timing is transmitted viaan associated control channel.
 3. The mobile station according to claim1, wherein the transmission timing is transmitted via an associatedphysical channel commonly used during a handover.
 4. The mobile stationaccording to claim 1, wherein the transmission timing and a mobilestation identifier is transmitted via a control channel commonly usedamong multiple mobile stations.
 5. A base station comprising: acontroller adapted to determine a transmission timing based onscheduling conducted upon a data transmission request from a mobilestation, a transmitter adapted to transmit, to the mobile station, thetransmission timing; and a receiver adapted to receive data from themobile station in accordance with the transmission timing.
 6. The basestation according to claim 5, further comprising: a selectioncombination unit adapted to selectively combine data forwarded fromanother base station.
 7. The base station according to claim 6, furthercomprising: a retransmission request notifying unit issuing aretransmission request to the mobile station if an error is detected inthe received data and the data is not forwarded from another basestation.
 8. A base station comprising: a receiver adapted to receivedata in accordance with a transmission timing transmitted from a mobilestation; and a packet forwarding unit adapted to forward decoded data toa first base station for the mobile station if no error is detected inthe data.
 9. A method for a mobile station comprising: transmitting adata transmission request; transmitting, to a first base station and asecond base station, a transmission timing transmitted from the firstbase station; and transmitting data to the first base station and thesecond base station based on the transmission timing.